Packet filtering is used in the first generation of firewalls and does not keep track of the state of a connection. Stateful packet filtering does. Source: WALLHOFF, John, CISSP Summary 2002, April 2002, CBK#2 Telecommunications and Network Security (page 6), /Documents/CISSP_Summary_2002/index.html.

It consists of a hybrid encryption scheme in sealing a message, by encrypting the
data and sending both it and a protected form of the key to the intended recipient, so that one else
can open the message.
In PKCS #7, it means first encrypting the data using a symmetric encryption algorithm and a
secret key, and then encrypting the secret key using an asymmetric encryption algorithm and the
public key of the intended recipient.
Source: SHIREY, Robert W., RFC2828: Internet Security Glossary, may 2000.

RAID level 5 stripes data and parity at block level across all the drives in the set.
A RAID 5 uses block-level striping with parity data distributed across all member disks.
RAID 5 has achieved popularity because of its low cost of redundancy. This can be seen by comparing the number of drives needed to achieve a given capacity.
For example, four 1 TB drives can be made into two separate 1 TB redundant arrays under
RAID 1 or 2 TB under RAID 1+0, but the same four drives can be used to build a 3 TB array under RAID 5.
Although RAID 5 may be implemented in a disk controller, some have hardware support for parity calculations (hardware RAID cards with onboard processors) while some use the main system processor (a form of software RAID in vendor drivers for inexpensive controllers).
Many operating systems also provide software RAID support independently of the disk controller, such as Windows Dynamic Disks, Linux mdadm, or RAID-Z. In most implementations, a minimum of three disks is required for a complete RAID 5 configuration.
Please see the reference below for a lot more details about all of the types of raid. For the purpose of the exam you have to be familiar with level zero to five, and combinations such as RAID 10 and RAID 50.
The following are incorrect answers:
RAID 1 : an exact copy (or mirror) of a set of data on two disks. This is useful when read performance or reliability is more important than data storage capacity. Such an array can only be as big as the smallest member disk. A classic RAID 1 mirrored pair contains two disks over a single disk. Since each member contains a complete copy and can be addressed independently, ordinary wear-and-tear reliability is raised by the power of the number of self-contained copies.
RAID 2 : stripes data at the bit (rather than block) level, and uses a Hamming code for error correction. The disks are synchronized by the controller to spin at the same angular orientation (they reach Index at the same time), so it generally cannot service multiple requests simultaneously. Extremely high data transfer rates are possible. This is the only original level of RAID that is not currently used.
All hard disks eventually implemented Hamming code error correction. This made RAID 2 error correction redundant and unnecessarily complex. Like RAID 3, this level quickly became useless and is now obsolete. There are no commercial applications of RAID 2.
RAID 4 : uses block-level striping with a dedicated parity disk. This allows each member of the set to act independently when only a single block is requested.
Reference(s) use for this question:
http://en.wikipedia.org/wiki/Standard_RAID_levels